Compositions for high temperature catalysis

ABSTRACT

Ceramic compositions with catalytic activity are provided, along with methods for using such catalytic ceramic compositions. The ceramic compositions correspond to compositions that can acquire increased catalytic activity by cyclic exposure of the ceramic composition to reducing and oxidizing environments at a sufficiently elevated temperature. The ceramic compositions can be beneficial for use as catalysts in reaction environments involving swings of temperature and/or pressure conditions, such as a reverse flow reaction environment. Based on cyclic exposure to oxidizing and reducing conditions, the surface of the ceramic composition can be converted from a substantially fully oxidized state to various states including at least some dopant metal particles supported on a structural oxide surface.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Application No.62/712,142 filed Jul. 30, 2018, which is herein incorporated byreference in its entirety.

FIELD

This invention relates to compositions suitable for use as catalyticmonoliths in high temperature environments.

BACKGROUND

Reverse flow reactors are an example of a reactor type that isbeneficial for use in processes with cyclic reaction conditions. Forexample, due to the endothermic nature of reforming reactions,additional heat needs to be introduced on a consistent basis into thereforming reaction environment. Reverse flow reactors can provide anefficient way to introduce heat into the reaction environment. After aportion of the reaction cycle used for reforming or another endothermicreaction, a second portion of the reaction cycle can be used forcombustion or another exothermic reaction to add heat to the reactionenvironment in preparation for the next reforming step. U.S. Pat. Nos.7,815,873 and 8,754,276 provide examples of using reverse flow reactorsto perform various endothermic processes in a cyclic reactionenvironment.

Endothermic reactions such as reforming can also benefit from having asubstantial amount of available catalytic surface area. Ceramic monolithstructures are an example of a type of structure that can provide a highavailable surface area. One option can be to use a monolithcorresponding to a packed array of cells or channels that the reactantgases pass through. Typically such monoliths are made of a singlecomposition, such as alumina. Washcoats are added to such monoliths toprovide catalytic activity.

SUMMARY

In various aspects, methods for reforming a hydrocarbon-containingstream are provided. The methods include exposing an initial compositioncomprising 0.1 wt % or more of at least one dopant metal oxide and 50 wt% to 99 wt % of one or more structural oxides to a reducing environment.The reducing environment can include a temperature of 500° C. to 1400°C. This can result in formation of a catalyst composition comprisingdopant metal particles supported on the one or more structural oxides.The one or more dopant metals can correspond to dopant metal oxideshaving a Gibbs free energy of formation at 800° C. that is greater thana Gibbs free energy of formation at 800° C. for the one or morestructural oxides by 200 kJ/mol or more. Optionally, the particles ofthe one or more dopant metals can have an average characteristic lengthof 10 μm or less. The dopant metal oxide can correspond to an oxide ofNi, Rh, Ru, Pd, Pt, Ir, or a combination thereof. The catalystcomposition can then be exposed to an oxidizing environment including atemperature of 500° C. to 1400° C. A hydrocarbon-containing stream canthen be exposed to the catalyst composition in the presence of at leastone of H₂O and CO₂ under reforming conditions comprising a temperatureof 500° C. or more to form a reformed product comprising H₂. Theexposing the hydrocarbon-containing stream to the catalyst compositioncan be performed after the exposing the catalyst composition to theoxidizing environment. The catalyst composition can then be exposed to astream comprising fuel and 0.1 vol % or more of O₂ under combustionconditions to heat an environment for the catalytic composition to atemperature of 500° C. or more.

Additionally or alternately, in various aspects a method for reforming ahydrocarbon-containing stream is provided. The method can includeintroducing a hydrocarbon-containing stream into a first end of areactor. The reactor can include a monolith that includes a catalystcomposition. The catalyst composition can correspond to 0.1 wt % or moreof dopant metal particles supported on 50 wt % to 99 wt % of one or morestructural oxides. The one or more dopant metals can correspond todopant metal oxides having a Gibbs free energy of formation at 800° C.that is greater than a Gibbs free energy of formation at 800° C. for theone or more structural oxides by 200 kJ/mol or more. Optionally, theparticles of the one or more dopant metals having an averagecharacteristic length of 10 μm or less. The dopant metal oxide cancorrespond to an oxide of Ni, Rh, Ru, Pd, Pt, Ir, or a combinationthereof. The hydrocarbon-containing stream can be exposed to thecatalyst composition in the presence of at least one of H₂O and CO₂under reforming conditions comprising a temperature of 800° C. or moreto form a reformed product comprising H₂. At least a portion of thereformed product can be withdrawn from a first location different fromthe first end of the reactor. A regeneration stream including fuel and astream including O₂ can then be introduced into the reactor. At least aportion of the stream comprising fuel and/or the stream comprising O₂can be introduced into a second end of the reactor. The streamcomprising fuel and the stream comprising oxygen can then be combustedunder combustion conditions to form a combustion product stream. Thecombustion product stream can be exposed to the catalyst composition totransfer heat to the catalyst composition. At least a portion of thecombustion product stream can then be withdrawn from the reactor.

In some aspects, the particles of one or more dopant metals cancorrespond to 1.0 wt % or more of Ni particles. Additionally oralternately, the one or more structural oxides can correspond to Al₂O₃.In such aspects, the catalytic composition can optionally furtherinclude NiO, NiAl₂O₄, or a combination thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically shows an example of operation of a reverse flowreactor.

FIG. 2 schematically shows an example of a reverse flow reactor.

FIG. 3 shows an SEM image of a ceramic honeycomb monolith composed of adopant oxide (NiO) and one or more structural oxides (including Al₂O₃).

FIG. 4 shows an SEM image of a portion of the honeycomb monolith athigher magnification.

FIG. 5 shows an X-ray diffraction spectrum obtained on the portion ofthe honeycomb monolith shown in FIG. 4.

FIG. 6 shows an SEM image of a portion of the honeycomb monolith afterexposure to a cyclic reaction environment.

FIG. 7 shows an Energy dispersive X-ray spectroscopy spectrum of thehoneycomb monolith shown in FIG. 6.

FIG. 8 shows a transmission electron microscope (TEM) image of anotherportion of the honeycomb monolith after exposure to a cyclic reactionenvironment.

DETAILED DESCRIPTION OF THE EMBODIMENTS

All numerical values within the detailed description and the claimsherein are modified by “about” or “approximately” the indicated value,and take into account experimental error and variations that would beexpected by a person having ordinary skill in the art.

Overview

In various aspects, ceramic compositions with catalytic activity areprovided, along with methods for using such catalytic ceramiccompositions. The ceramic compositions correspond to compositions thatcan acquire increased catalytic activity by cyclic exposure of theceramic composition to reducing and oxidizing environments at asufficiently elevated temperature. The ceramic compositions can bebeneficial for use as catalysts in reaction environments involvingswings of temperature and/or pressure conditions. For example, a ceramiccomposition formed from starting materials including nickel oxide andaluminum oxide can provide catalytic activity for reforming in a reverseflow reforming reaction environment. Based on cyclic exposure tooxidizing and reducing conditions, the surface of the ceramiccomposition can be converted from a substantially fully oxidized state,such as a combination of oxides including NiAl₂O₄ and Al₂O₃, to variousstates including at least some Ni metal supported on a surface includingAl₂O₃.

In contrast to conventional monoliths, the compositions described hereincan include a plurality of components, so that the compositioncorresponds to a doped ceramic composition. The ceramic composition caninclude at least one dopant oxide and one or more structural oxides thatare thermodynamically more stable than the dopant oxide(s). The dopantoxide(s) can correspond to an oxide of the catalytic metal(s). Afterforming and sintering the ceramic composition, the ceramic compositioncan be exposed to reducing conditions. Under the reducing conditions, aportion of the dopant oxide at the surface of the composition can beunexpectedly converted to the dopant metal particles. This is asurprising outcome that can be achieved by selecting the dopant oxide tobe thermodynamically less stable (i.e., smaller magnitude Gibbs freeenergy of formation) than the structural oxide(s) in the composition.Because the Gibbs free energy of formation for dopant oxides andstructural oxides is a negative value, the Gibbs free energy offormation for a dopant oxide is greater (less negative) than the Gibbsfree energy of formation for a structural oxide. If only reducingconditions are used, however, the dopant metal particles can quicklydeactivate. Without being bound by any particular theory, it is believedthat this deactivation is due in part to the tendency of the dopantmetal particles to coalesce to form rather large metal particles. Bysubsequently exposing the catalytic composition (including the dopantmetal particles) to oxidizing conditions on a periodic or cyclic basis,the dopant metal particles can unexpectedly provide catalytic activityon an ongoing basis. It is believed that part of the unexpected activityis due to cycling between oxidizing and reducing conditions, which canreduce or minimize the tendency of the dopant metal particles tocoalesce.

After metal particles are formed, it is noted that cycling betweenoxidizing and reducing conditions can potentially provide ongoingoxidation and reduction of the metal particles. Thus, after formingmetal particles in an initial reducing step, a subsequent oxidation stepcan partially oxidize at least a portion of the metal particles. Theresulting metal oxide particles can then be at least partially reducedto metal particles in a subsequent reducing step.

In some aspects, the porosity of the monolith material can be sufficientso that substantially all of the monolith can be converted to dopantmetal particles and structural oxides/other structural materials.Depending on the porosity of the monolith material and the thickness ofthe cell walls, the monolith can be substantially converted during theinitial reducing step, or the conversion of substantially all of themonolith can occur over the course of a plurality of oxidizing/reducingcycles. In aspects where a plurality of oxidizing and reducing cyclesare needed to convert additional portions of the monolith to dopantmetal particles and structural oxides (and optionally structuralmaterials), a first portion of dopant metal particles can form during aninitial reducing step while additional portions (such as a secondportion, third portion, etc.) of dopant metal particles can form insubsequent reducing steps. These additional metal particles can alsoundergo cyclic oxidation and reducing upon continued exposure to thecyclic process conditions.

In addition to providing catalytic activity, in some aspects the ceramiccomposition including a plurality of components can provide an increasedheat capacity relative to conventional single component monoliths.Optionally, additional materials can be included in the ceramiccomposition, such as silica-containing materials, to provide additionalstability and/or additional heat capacity for the composition. Invarious aspects, the volumetric heat capacity of the monolith materialcan be 1.4 J/cm³ or more, or 1.7 J/cm³ or more, or 2.0 J/cm³ or more, or2.2 J/cm³ or more. Higher volumetric heat capacities are generallyfavorable, so the volumetric heat capacity can be as large as desired,such as up to 6.0 J/cm³ or more.

More generally, a monolith formed from a ceramic composition that hascatalytic activity can be used in a wide variety of reactionenvironments that include both reducing and oxidizing conditions attemperatures between 500° C. and 1400° C. A possible but not exhaustivelist of chemistries include water gas shift (WGS), oxidative paraffincoupling, paraffin dehydrogenation to olefins, oxidative dehydrogenationof paraffins to olefins, methane/ethane dehydrogenation to aromatics,selective ammonia oxidation to NO, ammonia synthesis, hydrogen cyanideproduction, methanol oxidation to formaldehyde, catalytic combustion,solid oxide fuel cells, and combinations thereof.

In order to prepare a composition for introduction into a reactor (i.e.,the reactor where the cyclic reaction environment will be provided), aceramic composition can be formed into any convenient shape. One optioncan be to extrude or otherwise form a monolith from the ceramiccomposition. In some aspects, a monolith can include a large pluralityof cells or passages that reactant gases can pass through. Because thecomposition itself can provide catalytic activity, the composition canpotentially be used without a washcoat. This can allow smaller cellsizes to be used and/or a higher density of cells (such as higher cellsper square inch) while still maintaining a desirable pressure dropacross the monolith. Conventionally, addition of a washcoat to amonolith can reduce the available cross-section within a cell forpassage of gases. In order to account for this, conventional monolithstructures are designed with cell sizes large enough to accommodate thepresence of a washcoat while still maintaining a desirable pressuredrop. In various aspects, because the composition provides catalyticactivity after exposure to the cyclic reaction environment, a washcoatis not necessary for a monolith formed from the composition. This canallow a monolith to be formed with a higher density of cells and/orsmaller cells while still providing desirable flow conditions for thegas phase reactants.

In other aspects, a washcoat can be used in combination with thecomposition to provide a monolith (or other catalytic structure) withfurther enhanced activity.

Composition Prior to Exposure to Reducing Environment

In various aspects, the ceramic composition can include at least onedopant oxide and one or more structural oxides that arethermodynamically more stable than the dopant oxide. At least one of theoxides in the ceramic composition corresponds to a dopant oxide. Themetal (or metals) of the dopant oxide(s) corresponds to the metal thatwill be reduced during exposure to the reducing conditions to form metalparticles on the ceramic surface. To achieve this, the dopant can beselected to be less thermodynamically stable than the structuraloxide(s) present in the composition. In this discussion, a dopant oxidewith a lower thermodynamic stability than a structural oxide correspondsto a dopant oxide with a smaller magnitude for the Gibbs free energy offormation (AG) at a temperature of 800° C. and in the presence ofoxygen. Such combinations of dopant oxides and structural oxides can beidentified, for example, using an Ellingham diagram.

In various aspects, suitable combinations of dopant oxides andstructural oxides can correspond to any combination where the differenceof the Gibbs free energy of formation of the dopant oxide and thestructural oxide oxides is greater than 200 kJ/mol at a temperature of800° C., or greater than 300 kJ/mol, or greater than 400 kJ/mol. As anon-limiting example, the Gibbs free energy of formation of NiO from Niis ˜−300 kJ/mol at 800° C. and the Gibbs free energy of formation ofAl₂O₃ from Al is ˜−900 kJ/mol at 800° C. Since the difference in Gibbsfree energy of formation is roughly 600 kJ/mol, NiO and Al₂O₃ can be asuitable combination of a dopant oxide and a structural oxide. Asanother non-limiting example, the Gibbs free energy of formation of CoOfrom Co is ˜−300 kJ/mol at 800° C. and the Gibbs free energy offormation of TiO₂ from Ti is ˜−700 kJ/mol at 800° C. Since thedifference in Gibbs free energy of formation is roughly 400 kJ/mol, CoOand TiO₂ can be a suitable combination of a dopant oxide and astructural oxide. As yet another non-limiting example, the Gibbs freeenergy of formation of Fe₂O₃ from Fe is ˜−200 kJ/mol at 800° C. and theGibbs free energy of formation of SiO₂ from Si is ˜−700 kJ/mol at 800°C. Since the difference in Gibbs free energy of formation is roughly 500kJ/mol, Fe₂O₃ and SiO₂ can be a suitable combination of a dopant oxideand a structural oxide.

In the ceramic composition, the metal of the structural oxide can bepresent in an excess molar amount relative to the amount of dopant. Insome aspects, this can correspond to having a greater number of moles ofthe metal(s) of the structural oxide relative to the metal(s) of thedopant oxide.

In other aspects, a dopant oxide and a structural oxide can form acombined oxide phase. For example, in an example where NiO is a dopantoxide and Al₂O₃ is a structural oxide, the dopant oxide and structuraloxide can combine to form nickel aluminate (NiAl₂O₄). When such acombined oxide phase can be formed from the dopant oxide and thestructural oxide, the molar amount of the metal in the structural oxidecan be present in an excess molar amount relative to the amount ofstructural oxide needed to incorporate all of the dopant oxide (such asNiO) as part of a combined oxide (such as NiAl₂O₄). In the case of NiOand Al₂O₃, the molar ratio of Al to Ni in NiAl₂O₄ is 2.0. Thus, in sucha ceramic composition, the molar ratio of Al to Ni can be greater than2.0, such as 2.5 or more, or 3.0 or more, or 4.0 or more, or possiblystill higher. It is noted that having a molar ratio of Al to Ni of 2.5corresponds to having 25% more Al than is needed for full incorporationof the Ni into the combined oxide. In other words, there is a molarexcess of Al of 25%. Similarly, having a molar ratio of Al to Ni of 3.0corresponds to having 50% excess Al, and having a molar ratio of 4.0corresponds to having 100% excess Al. It is noted that when a mixedoxide phase is formed between a dopant oxide and a first structuraloxide, other structural oxides may be present that do not participate informing the mixed oxide phase. For example, in the nickel oxide andalumina example described above, silica and/or titania can be present insmaller molar amounts than alumina. The presence of the silica and/ortitania does not modify the calculation regarding the amount of excessalumina. The amount of excess structural oxide is determined based onlyon the structural oxides that participate in the mixed oxide phase.

More generally, the molar amount of metal from the structural oxide canbe at least 5% greater than the amount needed stoichiometrically tofully incorporate the dopant metal into the mixed oxide (i.e., a molarexcess of 5% or more), or at least 10% greater (molar excess of 10% ormore), or at least 20% greater (molar excess of 20% or more), or atleast 50% greater (molar excess of 50% or more), such as up to 500%greater (molar excess of 500% or more) or possibly still higher.

In various aspects, suitable dopant metals can include, but are notlimited to, Ni, Co, Fe, Pd, Rh, Ru, Pt, Ir, Cu, Ag, Au, Zr, Cr, Ti, V,and combinations thereof. The dopant metal can be selected based on thedesired type of catalytic activity. For example, for reforming ofhydrocarbons in the presence of H₂O and/or CO₂ to make hydrogen, Ni, Rh,Ru, Pd, Pt, Ir, and a combination of thereof can be suitable dopantmetals. The weight of dopant oxide in the ceramic composition can rangefrom 0.1 wt % to 50 wt %, or 1.0 wt % to 50 wt %, or 5.0 wt % to 40 wt%, or 10 wt % to 40 wt %, relative to the total weight of the ceramiccomposition. In some aspects where the dopant metal corresponds to aprecious metal or noble metal, the weight of dopant oxide in the ceramiccomposition can range from 0.1 wt % to 10 wt %, or 0.1 wt % to 5.0 wt %,or 1.0 wt % to 10 wt %.

In various aspects, suitable metals for the structural oxide in theceramic composition can include, but are not limited to, Al, Si, Ca, Mg,K, Na, Y, Zr, Hf, Ti, Cr, Mn, La, Ni, Co, and combinations thereof. Themetal(s) for the structural oxide can be selected so that the structuraloxide substantially does not convert to metallic form under the reducingconditions present in the cyclic reaction environment. As an example,when the dopant oxide is NiO, one option for a structural oxide isAl₂O₃. Another example of a suitable structural oxide in combinationwith NiO as the dopant oxide is a mixture of Al₂O₃ with SiO₂ and/orTiO₂. In such an example, SiO₂ can combine with Al₂O₃ to form a mullitephase that has increased resistance to thermal shock and/or mechanicalfailure. Additionally or alternately, in such an example, TiO₂ can beadded to facilitate extrusion and sintering to form a ceramic monolith.

In some embodiments, a ceramic composition can further include additivecomponents. Such additive components can correspond to additionalstructural components within the ceramic composition. For example, aceramic composition may further comprise one or more silicatescomprising a metal selected from the group consisting of Al, Si, Ca, Mg,K, Na, Y, Zr, Hf, Ti, Cr, Mn, Fe, Ni, Co, and mixtures thereof. Onenon-limiting example is bentonite, which is an aluminum phyllosilicateclay composed mostly of montmorillonite. The different types ofbentonite are each named after the respective dominant element, such aspotassium (K), sodium (Na), calcium (Ca), and aluminum (Al). Forexample, the chemical formula of sodium bentonite is Al₂H₂Na₂O₁₃Si₄.Some hydroxyl ions (OH—) can be present in silicates, but under hightemperature calcination and sintering conditions, such hydroxyl groupscan be converted to oxide form. Bentonite can be beneficial infabrication of doped ceramic monoliths due to the ability of bentoniteto facilitate extrusion.

In some optional aspects, a doped ceramic composition can include freesilica (Sift). In some aspects, the amount of a free silica in a dopedceramic composition can be 10 wt % or less relative to a weight of thedoped ceramic composition, or 5.0 wt % or less, or 2.0 wt % or less,such as down to 0.1 wt %, or down to 0.01 wt %, or possibly still lower.For example, the amount of free silica can be 0.1 wt % to 10 wt %, or1.0 wt % to 10 wt %, or 0.1 wt % to 5.0 wt %, or 0.1 wt % to 2.0 wt %.Such free silica can correspond to silica that is present in the dopedceramic composition in the form of SiO₂, as opposed to silica present inthe composition in the form of mullite (a solid solution of alumina andsilica). Such free silica may be vaporized during the reforming processand deposited on active sites of the doped ceramic composition. In otheraspects, a doped ceramic composition can include no silica, or caninclude silica only as silica incorporated as part of a solid solutionor other mixed oxide.

Monolith Structure

In various aspects, the ceramic composition that is composed of at leastone dopant oxide and at least one structural oxide (and optionally otherstructural components) may be prepared by manufacturing techniques suchas but not limited to conventional ceramic powder manufacturing andprocessing techniques, e.g., mixing, milling, degassing, kneading,pressing, extruding, casting, drying, calcining, and sintering. Thestarting materials can correspond to a suitable ceramic powder and anorganic binder powder in a suitable volume ratio. Certain process stepsmay be controlled or adjusted to obtain the desired grain size andporosity range and performance properties, such as by inclusion ofvarious manufacturing, property adjusting, and processing additives andagents as are generally known in the art. For example, the two or moretypes of oxide powders may be mixed in the presence of an organic binderand one or more appropriate solvents for a time sufficient tosubstantially disperse the powders in each other. As another example,precursors of a dopant oxide, a stable oxide, or both may be dissolvedin water at a desired ratio, spray dried, and calcined to make a mixedpowder. Such precursors include (but are not limited to) chlorides,sulfates, nitrates, and mixtures thereof. The calcined powder can befurther mixed in the presence of an organic binder and appropriatesolvent(s) to make a mixed “dough”. Then, the mixed “dough” of materialscan be placed in a die or form, extruded, dried or otherwise formed intoa desired shape. The resulting “green body” can then be sintered attemperatures in the range of about 1200° C.-1700° C. for at least tenminutes, such as from 10 minutes to 10 hours, or possibly from 10minutes up to 48 hours or still longer.

The sintering operation may be performed in an oxidizing atmosphere,reducing atmosphere, or inert atmosphere, and at ambient pressure orunder vacuum. For example, the oxidizing atmosphere could be air oroxygen, the inert atmosphere could be argon, and a reducing atmospherecould be hydrogen, CO/CO₂ or H₂/H₂O mixtures. Thereafter, the sinteredbody is allowed to cool, typically to ambient conditions. The coolingrate may also be controlled to provide a desired set of grain and porestructures and performance properties in the particular component.

It has been unexpectedly discovered that limiting the maximum porosityin the final sintered body tends to effectively, if not actually, limitinterconnectivity of the pore spaces with other pore spaces to an extentthat increases or maximizes volumetric heat capacity of the sinteredbody. The porosity ranges for a doped ceramic material and componentscan depend upon the desired final component performance properties, butare within a range defined by one or more of the minimum porosity valuesand one or more of the maximum porosity values, or any set of values notexpressly enumerated between the minimums and maximums. Examples ofsuitable porosity values are 0 vol % to 20 vol % porosity, or 0 vol % to15 vol %, or 0 vol % to 10 vol %, or 0 vol % to 5 vol %.

The sintered monolith and/or other formed ceramic structure can have anyconvenient shape suitable for use as a catalytic surface. An example ofa monolith can be an extruded honeycomb monolith. Honeycomb monolithscan be extruded structures that comprise many (e.g., a plurality,meaning more than one) small gas flow passages or conduits, arranged inparallel fashion with thin walls in between. A small reactor may includea single monolith, while a larger reactor can include a number ofmonoliths, while a still larger reactor may be substantially filled withan arrangement of many honeycomb monoliths. Each monolith may be formedby extruding monolith blocks with shaped (e.g., square or hexagonal)cross-section and two- or three-dimensionally stacking such blocksabove, behind, and beside each other. Monoliths can be attractive asreactor internal structures because they provide high heat transfercapacity with minimum pressure drop.

In some aspects, honeycomb monoliths can be characterized as having openfrontal area (or geometric void volume) between 25% and 55%, and havingconduit density between 50 and 2000 pores or cells per square inch(CPSI), or between 100 and 900 cells per square inch, or between 100cells per square inch to 600 cells per square inch. For example, in oneembodiment, the conduits may have a diameter/characteristic cell sidelength of only a few millimeters, such as on the order of roughly onemillimeter. Reactor media components, such as the monoliths oralternative bed media, can provide for channels that include a packingwith an average wetted surface area per unit volume that ranges from 50ft⁻¹ to 3000 ft⁻¹ (˜0.16 km⁻¹ to ˜10 km⁻¹), or from 100 ft⁻¹ to 2500ft⁻¹ (˜0.32 km⁻¹ to ˜8.2 km⁻¹), or from 200 ft⁻¹ to 2000 ft⁻¹ (˜0.65km⁻¹ to ˜6.5 km⁻¹), based upon the volume of the first reactor that isused to convey a reactant. These relatively high surface area per unitvolume values can aid in achieving a relatively quick change in thetemperature through the reactor, such as generally illustrated by therelatively steep slopes in the exemplary temperature gradient profilegraphs shown in FIG. 1(a) or 1(b) of FIG. 1.

Reactor media components can also provide for channels that include apacking that includes a high volumetric heat transfer coefficient (e.g.,0.02 cal/cm³s° C. or more, or 0.05 cal/cm³s° C. or more, or 0.10cal/cal/cm³s° C. or more); that have low resistance to flow (lowpressure drop); that have an operating temperature range consistent withthe highest temperatures encountered during regeneration; that have highresistance to thermal shock; and/or that have high bulk heat capacity(e.g., 0.10 cal/cm³s° C. or more, or 0.20 cal/cm³s° C. or more). As withthe high surface area values, these relatively high volumetric heattransfer coefficient values and/or other properties can aid in achievinga relatively quick change in the temperature through the reactor, suchas generally illustrated by the relatively steep slopes in the exemplarytemperature gradient profile graphs, such as in FIGS. 1(a) and 1(b) ofFIG. 1. The cited values are averages based upon the volume of reactorused for conveyance of a reactant.

In various aspects, adequate heat transfer rate can be characterized bya heat transfer parameter, ΔTHT, below 500° C., or below 100° C., orbelow 50° C. The parameter ΔTHT, as used herein, is the ratio of thebed-average volumetric heat transfer rate that is needed forrecuperation, to the volumetric heat transfer coefficient of the bed,hv. The volumetric heat transfer rate (e.g. cal/cm³ sec) that issufficient for recuperation can be calculated as the product of the gasflow rate (e.g. g/sec) with the gas heat capacity (e.g. cal/g° C.) anddesired end-to-end temperature change (excluding any reaction, e.g. °C.), and then this quantity can be divided by the volume (e.g. cm³) ofthe reactor (or portion of a reactor) traversed by the gas. Thevolumetric heat transfer coefficient of the bed, hv, can typically becalculated as the product of an area-based coefficient (e.g. cal/cm²s°C.) and a specific surface area for heat transfer (av, e.g. cm²/cm³),often referred to as the wetted area of the packing.

In some aspects, a washcoat can be added to the formed, sintered ceramiccomposition prior to exposing the composition to a reducing environmentto form dopant metal particles. A washcoat can allow the sinteredceramic composition to be impregnated with additional catalytic metal.Such additional catalytic metal can be the same as the dopant metal ordifferent.

One option for incorporating an additional catalytic metal into awashcoat can be to impregnate a catalyst support with the additionalcatalytic metal, such as by impregnation via incipient wetness. Theimpregnation can be performed with an aqueous solution of suitable metalsalt or other catalytic metal precursor, such as tetramineplatinumnitrate or rhodium nitrate hydrate. The impregnated support can then bedried and/or calcined for decomposition of the catalytic metalprecursor. A variety of temperature profiles can potentially be used forthe heating steps. One or more initial drying steps can be used fordrying the support, such as heating at a temperature from 100° C. to200° C. for 0.5 hours to 24 hours. A calcination to decompose thecatalytic metal precursor compound can be at a temperature of 200° C. to800° C. for 0.5 hours to 24 hours, depending on the nature of theimpregnated catalytic metal compound. Depending on the precursor for thecatalytic metal, the drying step(s) and/or the decomposing calcinationstep(s) can be optional. Examples of additional catalytic metals caninclude, but are not limited to, Ni, Co, Fe, Pd, Rh, Ru, Pt, Ir, Cu, Ag,Au, Zr, Cr, Ti, V, and combinations thereof.

The catalyst (including support and catalytic metal) can then be used inany convenient manner. In some aspects, the catalyst can be coated on astructure, such as a monolith structure that can reside within areactor. To form a washcoat solution, the catalyst can optionally becombined with a binder, such as an alumina binder. The mixture ofcatalyst and binder can then be added to water to form an aqueoussuspension having 10 wt % to 50 wt % solids. For example, the aqueoussuspension can include 10 wt % to 50 wt % solids, or 15 wt % to 40 wt %,or 10 wt % to 30 wt %. The amount of binder relative to the amount ofsolids can be any convenient amount, and the amount of binder can varydepending on the porosity and/or roughness. It is noted that smallerparticles may adhere to the monolith surface better in the initiallayer, so addition of a binder can assist with providing smallerparticle sizes in a mixture of catalyst and binder particles.Optionally, an acid can be added to the aqueous solution to reduce thepH so as to reduce or minimize agglomeration of the alumina catalystand/or binder particles. For example, acetic acid or another organicacid can be added to achieve a pH of 3 to 4. The suspension can then beball milled (or processed in another manner) to achieve a desiredparticle size for the catalyst particles, such as a particle size of 0.5μm to 5 μm. After milling, the solution can be stirred until time foruse so that the particles are distributed substantially uniformly in thesolution.

The washcoat solution can then be applied to a monolith structure toachieve a desired amount of catalyst (such as rhodium) on the monolithsurface. As an example, in one aspect a washcoat thickness of 10 micronswas achieved by forming a washcoat corresponding to 10 wt % of themonolith structure. Any convenient type of monolith structure can beused to provide a substantial surface area for support of the catalystparticles. The washcoat can be applied to the monolith to form cellshaving inner surfaces coated with the catalyst. One option for applyingthe washcoat can be to dip or otherwise submerge the monolith in thewashcoat. After clearing the cell channels of excess washcoat, themonolith can be dried and/or calcined. Drying can correspond to heatingat 100° C. to 200° C. for 0.5 hours to 24 hours, while calcining cancorrespond to heating at 200° C. to 800° C. for 0.5 hours to 24 hours.

Composition After Exposure to Cyclic Reaction Environment

After forming a ceramic composition into a desired structural form, suchas a monolith, the ceramic composition can be exposed to a reducingenvironment to form a catalytic composition including metal dopantparticles on the surface of the composition. The catalytic compositioncan then be used, for example, in a cyclic reaction environment.

The cyclic reaction environment can include exposing the ceramiccomposition to alternating periods of oxidizing conditions and reducingconditions at elevated temperatures. The elevated temperatures cancorrespond to temperatures of 500° C. to 1400° C., depending on thenature of the composition and the desired reaction. The nature of theoxidizing and reducing conditions can also vary depending on the desiredreaction. An example of reforming conditions can be steam reforming ordry reforming conditions for reforming of methane or other hydrocarbons.

When the ceramic composition is initially introduced into the reactor,the surface of the ceramic composition can correspond to various oxides.It has been unexpectedly discovered that initial exposure to a reducingenvironment followed by exposure to a cyclic reaction environmentincluding both reducing conditions and oxidizing conditions can increaseor enhance the catalytic activity of the ceramic composition. To achievethis enhanced catalytic activity, the composition can be exposed to atleast one time period of reducing environment to form dopant metalparticles on the surface of the composition. After the initial exposureto the reducing environment, the ceramic composition can becatalytically active, so long as the composition is exposed to a cyclicenvironment that provides both reducing and oxidizing conditions. Insome aspects, the catalytic activity can initially increase withcontinued exposure to the cyclic environment, and then eventually“line-out” or stabilize at an activity level over time. Suitable typesof reactors for providing the cyclic reaction environment can include,but are not limited to, reforming reactors, reverse flow reactors, andregenerative reactors.

During initial exposure to the reducing environment, at least a portionof the dopant oxide at and/or near the surface of the ceramiccomposition can be converted to dopant metal. The oxygen from the dopantoxide can be incorporated into the gas phase components of the reducingenvironment. This can result in formation of particles of the dopantmetal on the surface of the composition, such as metal microparticles ormetal nanoparticles. The oxygen from the dopant metal particles can beincorporated, for example, into the gas phase reaction productsgenerated by the reducing environment. For example, in a reducingenvironment that corresponds to a methane reforming environment, theoxygen from the dopant metal can partially oxidize a portion of themethane reforming products to form CO and/or H₂O. In some aspects, theinitial reducing conditions can correspond to conditions used only forthe initial reducing step. Alternatively, the reducing conditions cancorrespond to reaction environment conditions for the subsequentcycle(s) of reducing and oxidizing conditions. Examples of suitablereducing conditions for either the initial reducing exposure or for usein a cyclic reaction environment can include, but are not limited to,conditions for performing steam reforming of hydrocarbons, dry reformingof hydrocarbons, coal gasification, pyrolysis of hydrocarbons to formacetylene or olefins, and steam cracking. Examples of reducingenvironments include environments containing methane, ethane, propane,butane, higher C number paraffins, ethylene, propylene, butylene, higherC number olefins, acetylene, methylacetylene-propadiene (MAPD),hydrogen, carbon monoxide, hydrides, hydrogen sulfide, or combinationsthereof. It is noted that an environment include both 02 and a potentialreducing environment component generally corresponds to an oxidizingenvironment (such as a combustion environment), unless the 02 correspondto 5 mol % or less of the stoichiometric amount for combustion of thereducing environment component(s).

The particles of dopant metal formed on the structural oxide can have acharacteristic length of 10 μm or less, or 5.0 μm or less, or 2.5 μm orless, such as down to 0.01 μm or possibly still smaller. In thisdiscussion, the characteristic length for a particle is defined as thediameter of the smallest bounding sphere that can contain the particle.

After formation of particles of the dopant metal and/or at the end ofthe reducing portion of a reaction cycle, the ceramic composition can beexposed to an oxidizing environment. Without being bound by anyparticular theory, it is believed that the oxidizing environment canremove any coke that has accumulated on the dopant metal particlesand/or other active sites on the surface. Optionally, the oxidizingenvironment can also oxidize a portion of the dopant metal on thesurface, converting a portion of the dopant metal back into metal oxide.An example of an oxidizing environment can be a gas phase environmentincluding air or another gas phase composition that includes O₂. Moregenerally, examples of oxidizing environments include environmentscontaining oxygen (O₂), carbon dioxide, carbon monoxide, water,combustion byproducts, peroxide, ozone, permanganate, organic acids,halides, or combinations thereof. It is noted that formation ofcombustion byproducts may be performed in-situ, so that the oxidizingenvironment may also include a fuel, such as a hydrocarbon fuel. It isunderstood that a variety of oxidizing/reducing environment combinationsare potentially available for providing a cyclic reaction environment.

Process Example—Reverse Flow Reforming and Regeneration

A ceramic monolith that can be activated by reducing conditions andprovide catalytic activity under cyclic reaction conditions, asdescribed herein, can be suitable in some aspects for reforming ofhydrocarbons under steam reforming conditions in the presence of H₂O,under dry reforming conditions in the presence of CO₂, or underconditions where both H₂O and CO₂ are present in the reactionenvironment. As a general overview of operation during reforming in aswing reactor, such as a reverse flow reactor, a regeneration step orportion of a reaction cycle can be used to provide heat for the reactor.Reforming can then occur within the reactor during a reforming step orportion of the cycle, with the reforming reaction consuming heatprovided during the reactor regeneration step. During reactorregeneration, fuel and an oxidant are introduced into the reactor from aregeneration end of the reactor. The bed and/or monoliths in theregeneration portion of the reactor can absorb heat, but typically donot include a catalyst for reforming. As the fuel and oxidant passthrough the regeneration section, heat is transferred from theregeneration section to the fuel and oxidant. Combustion does not occurimmediately, but instead the location of combustion is controlled tooccur in a middle portion of the reactor. The flow of the reactantscontinues during the regeneration step, leading to additional transferof the heat generated from combustion into the reforming end of thereactor.

After a sufficient period of time, the combustion reaction is stopped.Any remaining combustion products and/or reactants can optionally bepurged. The reforming step or portion of the reaction cycle can thenstart. The reactants for reforming can be introduced into the reformingend of the reactor, and thus flow in effectively the opposite directionrelative to the flow during regeneration. The bed and/or monoliths inthe reforming portion of the reactor can include a catalyst forreforming. In various aspects, at least a portion of the catalyst cancorrespond to a catalyst formed from a ceramic composition as describedherein. As reforming occurs, the heat introduced into the reforming zoneduring combustion can be consumed by the endothermic reforming reaction.After exiting the reforming zone, the reforming products (and unreactedreactants) are no longer exposed to a reforming catalyst. As thereforming products pass through the regeneration zone, heat can betransferred from the products to the regeneration zone. After asufficient period of time, the reforming process can be stopped,remaining reforming products can optionally be collected or purged fromthe reactor, and the cycle can start again with a regeneration step.

The reforming reaction performed within the reactor can correspondreforming of methane and/or other hydrocarbons using steam reforming, inthe presence of H₂O; using dry reforming, in the presence of CO₂, orusing “bi” reforming in the presence of both H₂O and CO₂. Examples ofstoichiometry for steam, dry, and “bi” reforming of methane are shown inequations (1)-(3).Dry Reforming: CH₄+CO₂=2CO+2H₂  (1)Steam Reforming: CH₄+H₂O=CO+3H₂  (2)Bi Reforming: 3CH₄+2H₂O+CO₂=4CO+8H₂.  (3)

As shown in equations (1)-(3), dry reforming can produce lower ratios ofH₂ to CO than steam reforming. Reforming reactions performed with onlysteam can generally produce a ratio of H₂ to CO of around 3, such as 2.5to 3.5. By contrast, reforming reactions performed in the presence ofCO₂ can generate much lower ratios, possibly approaching a ratio of H₂to CO of roughly 1.0 or even lower. By using a combination of CO₂ andH₂O during reforming, the reforming reaction can potentially becontrolled to generate a wide variety of H₂ to CO ratios in a resultingsyngas.

It is noted that the ratio of H₂ to CO in a synthesis gas can also bedependent on the water gas shift equilibrium. Although the abovestoichiometry shows ratios of roughly 1 or roughly 3 for dry reformingand steam reforming, respectively, the equilibrium amounts of H₂ and COin a synthesis gas can be different from the reaction stoichiometry. Theequilibrium amounts can be determined based on the water gas shiftequilibrium, which relates the concentrations of H₂, CO, CO₂ and H₂Obased on the reactionH₂O+CO⇔H₂+CO₂  (4)

Most reforming catalysts, such as rhodium and/or nickel, can also serveas water gas shift catalysts. Thus, if reaction environment forproducing H₂ and CO also includes H₂O and/or CO₂, the initialstoichiometry from the reforming reaction may be altered based on thewater gas shift equilibrium. This equilibrium is also temperaturedependent, with higher temperatures favoring production of CO and H₂O.It is noted that higher temperatures can also improve the rate forreaching equilibrium. As a result, the ability to perform a reformingreaction at elevated temperatures can potentially provide severalbenefits. For example, instead of performing steam reforming in anenvironment with excess H₂O, CO₂ can be added to the reactionenvironment. This can allow for both a reduction in the ratio of H₂ toCO produced based on the dry reforming stoichiometry as well as areduction in the ratio of H₂ to CO produced based on the water gas shiftequilibrium. Alternatively, if a higher H₂ to CO ratio is desired, CO₂can be removed from the environment, and the ratio of H₂O to CH₄ (orother hydrocarbons) can be controlled to produce a desirable type ofsynthesis gas. This can potentially allow for generation of a synthesisgas having a H₂ to CO ratio of 0.1 to 15, or 0.1 to 3.0, or 0.5 to 5.0,or 1.0 to 10, by selecting appropriate amounts of feed components.

The reforming reactions shown in equations (1)-(3) are endothermicreactions. One of the challenges in commercial scale reforming can beproviding the heat for performing the reforming reaction in an efficientmanner while reducing or minimizing introduction of additionalcomponents into the desired synthesis gas product. Cyclic reactionsystems, such as reverse flow reactor systems, can provide heat in adesirable manner by having a cycle including a reforming step and aregeneration step. During the regeneration step, combustion can beperformed within a selected area of the reactor. A gas flow duringregeneration can assist with transferring this heat from the combustionzone toward additional portions of the reforming zone in the reactor.The reforming step within the cycle can be a separate step, so thatincorporation of products from combustion into the reactants and/orproducts from reforming can be reduced or minimized. The reforming stepcan consume heat, which can reduce the temperature of the reformingzone. As the products from reforming pass through the reactor, thereforming products can pass through a second zone that lacks a reformingor water gas shift catalyst. This can allow the reaction products tocool prior to exiting the reactor. The heat transferred from thereforming products to the reactor can then be used to increase thetemperature of the reactants for the next combustion or regenerationstep.

One common source for methane is natural gas. In some applications,natural gas, including associated hydrocarbon and impurity gases, may beused as a feed for the reforming reaction. The supplied natural gas alsomay be sweetened and/or dehydrated natural gas. Natural gas commonlyincludes various concentrations of associated gases, such as ethane andother alkanes, preferably in lesser concentrations than methane. Thesupplied natural gas may include impurities, such as H₂S and nitrogen.More generally, the hydrocarbon feed for reforming can include anyconvenient combination of methane and/or other hydrocarbons. Optionally,the reforming feed may also include some hydrocarbonaceous compounds,such as alcohols or mercaptans, which are similar to hydrocarbons butinclude one or more heteroatoms different from carbon and hydrogen. Insome aspects, an additional component present in the feed can correspondto impurities such as sulfur that can adsorb to the catalytic monolithduring a reducing cycle (such as a reforming cycle). Such impurities canbe oxidized in a subsequent cycle to form sulfur oxide, which can thenbe reduced to release additional sulfur-containing components (or otherimpurity-containing components) into the reaction environment.

In some aspects, the feed for reforming can include, relative to a totalweight of hydrocarbons in the feed for reforming, 5 wt % or more of C₂₊compounds, such as ethane or propane, or 10 wt % or more, or 15 wt % ormore, or 20 wt % or more, such as up to 50 wt % or possibly stillhigher. It is noted that nitrogen and/or other gases that arenon-reactive in a combustion environment, such as H₂O and CO₂, may alsobe present in the feed for reforming. In aspects where the reformercorresponds to an on-board reforming environment, such non-reactiveproducts can optionally be introduced into the feed, for example, basedon recycle of an exhaust gas into the reformer. Additionally oralternately, the feed for reforming can include 40 wt % or more methane,or 60 wt % or more, or 80 wt % or more, or 95 wt % or more, such ashaving a feed that is substantially composed of methane (98 wt % ormore). In aspects where the reforming corresponds to steam reforming, amolar ratio of steam molecules to carbon atoms in the feed can be 0.3 to4.0. It is noted that methane has 1 carbon atom per molecule whileethane has 2 carbon atoms per molecule. In aspects where the reformingcorresponds to dry reforming, a molar ratio of CO₂ molecules to carbonatoms in the feed can be 0.05 to 3.0.

Within the reforming zone of a reverse flow reactor, the temperature canvary across the zone due to the nature of how heat is added to thereactor and/or due to the kinetics of the reforming reaction. Thehighest temperature portion of the zone can typically be found near amiddle portion of the reactor. This middle portion can be referred to asa mixing zone where combustion is initiated during regeneration. Atleast a portion of the mixing zone can correspond to part of thereforming zone if a monolith with reforming catalyst extends into themixing zone. As a result, the location where combustion is startedduring regeneration can typically be near to the end of the reformingzone within the reactor. Moving from the center of the reactor to theends of the reactor, the temperature can decrease. As a result, thetemperature at the beginning of the reforming zone (at the end of thereactor) can be cooler than the temperature at the end of the reformingzone (in the middle portion of the reactor).

As the reforming reaction occurs, the temperature within the reformingzone can be reduced. The rate of reduction in temperature can be relatedto the kinetic factors of the amount of available hydrocarbons forreforming and/or the temperature at a given location within thereforming zone. As the reforming feed moves through the reforming zone,the reactants in the feed can be consumed, which can reduce the amountof reforming that occurs at downstream locations. However, the increasein the temperature of the reforming zone as the reactants move acrossthe reforming zone can lead to an increased reaction rate.

At roughly 500° C., the reaction rate for reforming can be sufficientlyreduced that little or no additional reforming will occur. As a result,in some aspects as the reforming reaction progresses, the beginningportion of the reforming zone can cool sufficiently to effectively stopthe reforming reaction within a portion of the reforming zone. This canmove the location within the reactor where reforming begins to alocation that is further downstream relative to the beginning of thereforming zone. When a sufficient portion of the reforming zone has atemperature below 500° C., or below 600° C., the reforming step withinthe reaction cycle can be stopped to allow for regeneration.Alternatively, based on the amount of heat introduced into the reactorduring regeneration, the reforming portion of the reaction cycle can bestopped based on an amount of reaction time, so that the amount of heatconsumed during reforming (plus heat lost to the environment) is roughlyin balance with the amount of heat added during regeneration. After thereforming process is stopped, any remaining synthesis gas product stillin the reactor can optionally be recovered prior to starting theregeneration step of the reaction cycle.

The regeneration process can then be initiated. During regeneration, afuel such as methane, natural gas, or Hz, and oxygen can be introducedinto the reactor and combusted. The location where the fuel and oxidantare allowed to mix can be controlled in any convenient manner, such asby introducing the fuel and oxidant via separate channels. By delayingcombustion during regeneration until the reactants reach a centralportion of the reactor, the non-reforming end of the reactor can bemaintained at a cooler temperature. This can also result in atemperature peak in a middle portion of the reactor. The temperaturepeak can be located within a portion of the reactor that also includesthe reforming catalyst. During a regeneration cycle, the temperaturewithin the reforming reactor can be increased sufficiently to allow forthe reforming during the reforming portion of the cycle. This can resultin a peak temperature within the reactor of 1100° C. or more, or 1200°C. or more, or 1300° C. or more, or potentially a still highertemperature.

The relative length of time and reactant flow rates for the reformingand regeneration portions of the process cycle can be selected tobalance the heat provided during regeneration with the heat consumedduring reforming. For example, one option can be to select a reformingstep that has a similar length to the regeneration step. Based on theflow rate of hydrocarbons, H₂O, and/or CO₂ during the reforming step, anendothermic heat demand for the reforming reaction can be determined.This heat demand can then be used to calculate a flow rate forcombustion reactants during the regeneration step. Of course, in otheraspects the balance of heat between reforming and regeneration can bedetermined in other manners, such as by determining desired flow ratesfor the reactants and then selecting cycle lengths so that the heatprovided by regeneration balances with the heat consumed duringreforming.

In addition to providing heat, the reactor regeneration step during areaction cycle can also allow for coke removal from the catalyst withinthe reforming zone. In various aspects, one or more types of catalystregeneration can potentially occur during the regeneration step. Onetype of catalyst regeneration can correspond to removal of coke from thecatalyst. During reforming, a portion of the hydrocarbons introducedinto the reforming zone can form coke instead of forming CO or CO₂. Thiscoke can potentially block access to the catalytic sites (such as metalsites) of the catalyst. In some aspects, the rate of formation can beincreased in portions of the reforming zone that are exposed to highertemperatures, such as portions of the reforming zone that are exposed totemperatures of 800° C. or more, or 900° C. or more, or 1000° C. ormore. During a regeneration step, oxygen can be present as thetemperature of the reforming zone is increased. At the temperaturesachieved during regeneration, at least a portion of the coke generatedduring reforming can be removed as CO or CO₂.

Due to the variation in temperature across the reactor, several optionscan be used for characterizing the temperature within the reactor and/orwithin the reforming zone of the reactor. One option for characterizingthe temperature can be based on an average bed or average monolithtemperature within the reforming zone. In practical settings,determining a temperature within a reactor requires the presence of ameasurement device, such as a thermocouple. Rather than attempting tomeasure temperatures within the reforming zone, an average (bed ormonolith) temperature within the reforming zone can be defined based onan average of the temperature at the beginning of the reforming zone anda temperature at the end of the reforming zone. Another option can be tocharacterize the peak temperature within the reforming zone after aregeneration step in the reaction cycle. Generally, the peak temperaturecan occur at or near the end of the reforming zone, and may be dependenton the location where combustion is initiated in the reactor. Stillanother option can be to characterize the difference in temperature at agiven location within the reaction zone at different times within areaction cycle. For example, a temperature difference can be determinedbetween the temperature at the end of the regeneration step and thetemperature at the end of the reforming step. Such a temperaturedifference can be characterized at the location of peak temperaturewithin the reactor, at the entrance to the reforming zone, at the exitfrom the reforming zone, or at any other convenient location.

In various aspects, the reaction conditions for reforming hydrocarbonscan include one or more of an average reforming zone temperature rangingfrom 400° C. to 1200° (or more); a peak temperature within the reformingzone of 800° C. to 1500° C.; a temperature difference at the location ofpeak temperature between the end of a regeneration step and the end ofthe subsequent reforming step of 25° C. or more, or 50° C. or more, or100° C. or more, or 200° C. or more, such as up to 800° C. or possiblystill higher; a temperature difference at the entrance to the reformingzone between the end of a regeneration step and the end of thesubsequent reforming step of 25° C. or more, or 50° C. or more, or 100°C. or more, or 200° C. or more, such as up to 800° C. or possibly stillhigher; and/or a temperature difference at the exit from the reformingzone between the end of a regeneration step and the end of thesubsequent reforming step of 25° C. or more, or 50° C. or more, or 100°C. or more, or 200° C. or more, such as up to 800° C. or possibly stillhigher.

With regard to the average reforming zone temperature, in variousaspects the average temperature for the reforming zone can be 500° C. to1500° C., or 400° C. to 1200° C., or 800° C. to 1200° C., or 400° C. to900° C., or 600° C. to 1100° C., or 500° C. to 1000° C. Additionally oralternately, with regard to the peak temperature for the reforming zone(likely corresponding to a location in the reforming zone close to thelocation for combustion of regeneration reactants), the peak temperaturecan be 800° C. to 1500° C., or 1000° C. to 1400° C., or 1200° C. to1500° C., or 1200° C. to 1400° C.

Additionally or alternately, the reaction conditions for reforminghydrocarbons can include a pressure of 0 psig to 1500 psig (10.3 MPa),or 0 psig to 1000 psig (6.9 MPa), or 0 psig to 550 psig (3.8 MPa); and agas hourly space velocity of reforming reactants of 1000 hr⁻¹ to 50,000hr⁻¹. The space velocity corresponds to the volume of reactants relativeto the volume of monolith per unit time. The volume of the monolith isdefined as the volume of the monolith as if it was a solid cylinder.

In some aspects, an advantage of operating the reforming reaction atelevated temperature can be the ability to convert substantially all ofthe methane and/or other hydrocarbons in a reforming feed. For example,for a reforming process where water is present in the reforming reactionenvironment (i.e., steam reforming or bi-reforming), the reactionconditions can be suitable for conversion of 10 wt % to 100 wt % of themethane in the reforming feed, or 20 wt % to 80 wt %, or 50 wt % to 100wt %, or 80 wt % to 100 wt %, or 10 wt % to 98 wt %, or 50 wt % to 98 wt%. Additionally or alternately, the reaction conditions can be suitablefor conversion of 10 wt % to 100 wt % of the hydrocarbons in thereforming feed, or 20 wt % to 80 wt %, or 50 wt % to 100 wt %, or 80 wt% to 100 wt %, or 10 wt % to 98 wt %, or 50 wt % to 98 wt %

In other aspects, for a reforming process where carbon dioxide ispresent in the reforming reaction environment (i.e., dry reforming orbi-reforming), the reaction conditions can be suitable for conversion of10 wt % to 100 wt % of the methane in the reforming feed, or 20 wt % to80 wt %, or 50 wt % to 100 wt %, or 80 wt % to 100 wt %, or 10 wt % to98 wt %, or 50 wt % to 98 wt %. Additionally or alternately, thereaction conditions can be suitable for conversion of 10 wt % to 100 wt% of the hydrocarbons in the reforming feed, or 20 wt % to 80 wt %, or50 wt % to 100 wt %, or 80 wt % to 100 wt %, or 10 wt % to 98 wt %, or50 wt % to 98 wt %.

In some alternative aspects, the reforming reaction can be performedunder dry reforming conditions, where the reforming is performed withCO₂ as a reagent but with a reduced or minimized amount of H₂O in thereaction environment. In such alternative aspects, a goal of thereforming reaction can be to produce a synthesis gas with a H₂ to COratio of 1.0 or less. In some aspects, the temperature during reformingcan correspond to the temperature ranges described for steam reforming.Optionally, in some aspects a dry reforming reaction can be performed ata lower temperature of between 500° C. to 700° C., or 500° C. to 600° C.In such aspects, the ratio of H₂ to CO can be 0.3 to 1.0, or 0.3 to 0.7,or 0.5 to 1.0. Performing the dry reforming reaction under theseconditions can also lead to substantial coke production, which canrequire removal during regeneration in order to maintain catalyticactivity.

Example of Reverse Flow Reactor Configuration

For endothermic reactions operated at elevated temperatures, such ashydrocarbon reforming, a reverse flow reactor can provide a suitablereaction environment for providing the heat for the endothermicreaction.

In a reverse flow reactor, the heat needed for an endothermic reactionmay be provided by creating a high-temperature heat bubble in the middleof the reactor. A two-step process can then be used wherein heat is (a)added to the reactor bed(s) or monolith(s) via in-situ combustion, andthen (b) removed from the bed in-situ via an endothermic process, suchas reforming, pyrolysis, or steam cracking. This type of configurationcan provide the ability to consistently manage and confine the hightemperature bubble in a reactor region(s) that can tolerate suchconditions long term. A reverse flow reactor system can allow theprimary endothermic and regeneration processes to be performed in asubstantially continuous manner.

A reverse flow reactor system can include first and second reactors,oriented in a series relationship with each other with respect to acommon flow path, and optionally but preferably along a common axis. Thecommon axis may be horizontal, vertical, or otherwise. During aregeneration step, reactants (e.g., fuel and oxygen) are permitted tocombine or mix in a reaction zone to combust therein, in-situ, andcreate a high temperature zone or heat bubble inside a middle portion ofthe reactor system. The heat bubble can correspond to a temperature thatis at least about the initial temperature for the endothermic reaction.Typically, the temperature of the heat bubble can be greater than theinitial temperature for the endothermic reaction, as the temperaturewill decrease as heat is transferred from the heat bubble in a middleportion of the reactor toward the ends of the reactor. In some aspects,the combining can be enhanced by a reactant mixer that mixes thereactants to facilitate substantially complete combustion/reaction atthe desired location, with the mixer optionally located between thefirst and second reactors. The combustion process can take place over along enough duration that the flow of first and second reactants throughthe first reactor also serves to displace a substantial portion, (asdesired) of the heat produced by the reaction (e.g., the heat bubble),into and at least partially through the second reactor, but preferablynot all of the way through the second reactor to avoid waste of heat andoverheating the second reactor. The flue gas may be exhausted throughthe second reactor, but preferably most of the heat is retained withinthe second reactor. The amount of heat displaced into the second reactorduring the regeneration step can also be limited or determined by thedesired exposure time or space velocity that the hydrocarbon feed gaswill have in the endothermic reaction environment.

After regeneration or heating the second reactor media (which caninclude and/or correspond to a ceramic catalyst composition as describedherein), in the next/reverse step or cycle, reactants for theendothermic reaction methane (and/or natural gas and/or anotherhydrocarbon) can be supplied or flowed through the second reactor, fromthe direction opposite the direction of flow during the heating step.For example, in a reforming process, methane (and/or natural gas and/oranother hydrocarbon) can be supplied or flowed through the secondreactor. The methane can contact the hot second reactor and mixer media,in the heat bubble region, to transfer the heat to the methane forreaction energy.

For some aspects, the basic two-step asymmetric cycle of a reverse flowregenerative bed reactor system is depicted in FIGS. 1(a) and 1(b) ofFIG. 1 in terms of a reactor system having two zones/reactors; a firstor recuperator/quenching zone (7) and a second or reaction zone (1).Both the reaction zone (1) and the recuperator zone (7) can containregenerative monoliths and/or other regenerative structures formed froma doped ceramic composition. Regenerative monoliths or otherregenerative structures, as used herein, comprise materials that areeffective in storing and transferring heat as well as being effectivefor carrying out a chemical reaction. The regenerative monoliths and/orother structures can correspond to any convenient type of material thatis suitable for storing heat, transferring heat, and catalyzing areaction. Examples of structures can include bedding or packing materialceramic beads or spheres, ceramic honeycomb materials, ceramic tubes,extruded monoliths, and the like, provided they are competent tomaintain integrity, functionality, and withstand long term exposure totemperatures in excess of 1200° C., or in excess of 1400° C., or inexcess of 1600° C., which can allow for some operating margin. In someaspects, the catalytic ceramic monolith and/or other catalytic ceramicstructure can be used without the presence of an additional washcoat.

To facilitate description of FIG. 1, the reactor is described hereinwith reference to a reforming reaction. It is understood that otherconvenient types of endothermic reactions can generally be performedusing a reverse flow reactor, such as the reactor shown in FIG. 1.

As shown in FIG. 1(a) of FIG. 1, at the beginning of the “reaction” stepof the cycle, a secondary end 5 of the reaction zone 1 (a.k.a. herein asthe second reactor) can be at an elevated temperature as compared to theprimary end 3 of the reaction zone 1, and at least a portion (includingthe first end 9) of the recuperator or quench zone 7 (a.k.a. herein asthe first reactor), can be at a lower temperature than the reaction zone1 to provide a quenching effect for the resulting product. In an aspectwhere the reactors are used to perform reverse flow reforming, amethane-containing reactant feed (or other hydrocarbon-containingreactant feed) can be introduced via a conduit(s) 15, into a primary end3 of the reforming or reaction zone 1. In various aspects, thehydrocarbon-containing reactant feed can also contain H₂O, CO₂, or acombination thereof.

The feed stream from inlet(s) 15 can absorb heat from reaction zone 1and endothermically react to produce the desired synthesis gas product.As this step proceeds, a shift in the temperature profile 2, asindicated by the arrow, can be created based on the heat transferproperties of the system. When the ceramic catalyst monolith/othercatalyst structure is designed with adequate heat transfer capability,this profile can have a relatively sharp temperature gradient, whichgradient can move across the reaction zone 1 as the reforming stepproceeds. In some aspects, a sharper temperature gradient profile canprovide for improved control over reaction conditions. In aspects whereanother type of endothermic reaction is performed, a similar shift intemperature profile can occur, so that a temperature gradient movesacross reaction zone 1 as the reaction step proceeds.

The effluent from the reforming reaction, which can include unreactedfeed components (hydrocarbons, H₂O, CO₂) as well as synthesis gascomponents, can exit the reaction zone 1 through a secondary end 5 at anelevated temperature and pass through the recuperator reactor 7,entering through a second end 11, and exiting at a first end 9. Therecuperator 7 can initially be at a lower temperature than the reactionzone 1. As the products (and optionally unreacted feed) from thereforming reaction pass through the recuperator zone 7, the gas can bequenched or cooled to a temperature approaching the temperature of therecuperator zone substantially at the first end 9, which in someembodiments can be approximately the same temperature as theregeneration feed introduced via conduit 19 into the recuperator 7during the second step of the cycle. As the reforming effluent is cooledin the recuperator zone 7, a temperature gradient 4 can be created inthe zone's regenerative bed(s) and can move across the recuperator zone7 during this step. The quenching can heat the recuperator 7, which canbe cooled again in the second step to later provide another quenchingservice and to prevent the size and location of the heat bubble fromgrowing progressively through the quench reactor 7. After quenching, thereaction gas can exit the recuperator at 9 via conduit 17 and can beprocessed for separation and recovery of the various components.

The second step of the cycle, referred to as the regeneration step, canthen begin with reintroduction of the first and second regenerationreactants via conduit(s) 19. The first and second reactants can passseparately through hot recuperator 7 toward the second end 11 of therecuperator 7, where they can be combined for exothermic reaction orcombustion in or near a central region 13 of the reactor system.

An example of the regeneration step is illustrated in FIG. 1(b) ofFIG. 1. Regeneration can entail transferring recovered sensible heatfrom the recuperator zone 7 to the reaction zone 1 to thermallyregenerate the reaction beds 1 for the subsequent reaction cycle.Regeneration gas/reactants can enter recuperator zone 7, such as viaconduit(s) 19, and flow through the recuperator zone 7 and into thereaction zone 1. In doing so, the temperature gradients 6 and 8 may moveacross the beds as illustrated by the arrows on the exemplary graphs inFIG. 1(b), similar to but in opposite directions to the graphs of thetemperature gradients developed during the reaction cycle in FIG. 1(a)of FIG. 1. Fuel and oxidant reactants may combust at a region proximateto the interface 13 of the recuperator zone 7 and the reaction zone 1.The heat recovered from the recuperator zone together with the heat ofcombustion can be transferred to the reaction zone, thermallyregenerating the regenerative reaction monoliths and/or beds 1 disposedtherein.

In some aspects, several of the conduits within a channel may convey amixture of first and second reactants, due at least in part to somemixing at the first end (17) of the first reactor. However, the numbersof conduits conveying combustible mixtures of first and second reactantscan be sufficiently low such that the majority of the stoichiometricallyreactable reactants will not react until after exiting the second end ofthe first reactor. The axial location of initiation of combustion orexothermic reaction within those conduits conveying a mixture ofreactants can be controlled by a combination of temperature, time, andfluid dynamics. Fuel and oxygen usually require a temperature-dependentand mixture-dependent autoignition time to combust. Still though, somereaction may occur within an axial portion of the conduits conveying amixture of reactants. However, this reaction can be acceptable becausethe number of channels having such reaction can be sufficiently smallthat there is only an acceptable or inconsequential level of effect uponthe overall heat balance within the reactor. The design details of aparticular reactor system can be selected so as to avoid mixing ofreactants within the conduits as much as reasonably possible.

FIG. 2 illustrates another exemplary reactor system that may be suitablein some applications for controlling and deferring the combustion offuel and oxidant to achieve efficient regeneration heat. FIG. 2 depictsa single reactor system, operating in the regeneration cycle. Thereactor system may be considered as comprising two reactors zones. Therecuperator 27 can be the zone primarily where quenching takes place andprovides substantially isolated flow paths or channels for transferringboth of the quenching reaction gases through the reactor media, withoutincurring combustion until the gasses arrive proximate or within thereactor core 13 in FIG. 1. The reformer 2 can be the reactor whereregeneration heating and methane (and/or hydrocarbon) reformationprimarily occurs, and may be considered as the second reactor forpurposes herein. Although the first and second reactors in the reactorsystem are identified as separately distinguishable reactors, it isunderstood that the first and second reactors may be manufactured,provided, or otherwise combined into a common single reactor bed,whereby the reactor system might be described as comprising merely asingle reactor that integrates both cycles within the reactor. The terms“first reactor” and “second reactor” can merely refer to the respectivezones within the reactor system whereby each of the regeneration,reformation, quenching, etc., steps take place and do not require thatseparate components be utilized for the two reactors. However, variousaspects can comprise a reactor system whereby the recuperator reactorincludes conduits and channels as described herein, and the reformerreactor may similarly possess conduits. Additionally or alternately,some aspects may include a reformer reactor bed that is arrangeddifferent from and may even include different materials from, therecuperator reactor bed.

As discussed previously, the first reactor or recuperator 27 can includevarious gas conduits 28 for separately channeling two or more gasesfollowing entry into a first end 29 of the recuperator 27 and throughthe regenerative bed(s) disposed therein. A first gas 30 can enter afirst end of a plurality of flow conduits 28. In addition to providing aflow channel, the conduits 28 can also comprise effective flow barriers(e.g., which effectively function such as conduit walls) to preventcross flow or mixing between the first and second reactants and maintaina majority of the reactants effectively separated from each other untilmixing is permitted. As discussed previously, each of the first andsecond channels can comprise multiple channels or flow paths. The firstreactor may also comprise multiple substantially parallel flow segments,each comprising segregated first and second channels.

In some aspects, the recuperator can be comprised of one or moreextruded honeycomb monoliths, as described above. Each monolith mayprovide flow channel(s) (e.g., flow paths) for one of the first orsecond reactants. Each channel preferably includes a plurality ofconduits. Alternatively, a monolith may comprise one or more channelsfor each reactant with one or more channels or groups of conduitsdedicated to flowing one or more streams of a reactant, while theremaining portion of conduits flow one or more streams of the otherreactant. It is recognized that at the interface between channels, anumber of conduits may convey a mixture of first and second reactant,but this number of conduits is proportionately small.

Alternative embodiments may use reactor media other than monoliths, suchas whereby the channel conduits/flow paths may include a more tortuouspathways (e.g. convoluted, complex, winding and/or twisted but notlinear or tubular), including but not limited to labyrinthine,variegated flow paths, conduits, tubes, slots, and/or a pore structurehaving channels through a portion(s) of the reactor and may includebarrier portion, such as along an outer surface of a segment or withinsub-segments, having substantially no effective permeability to gases,and/or other means suitable for preventing cross flow between thereactant gases and maintaining the first and second reactant gasessubstantially separated from each other while axially transiting therecuperator 27. Such other types of reactor media can be suitable, solong as at least a portion of such media can be formed by sintering aceramic catalytic composition as described herein, followed by exposingsuch media to reducing conditions to activate the catalyst. For suchembodiments, the complex flow path may create a lengthened effectiveflow path, increased surface area, and improved heat transfer. Suchdesign may be preferred for reactor embodiments having a relativelyshort axial length through the reactor. Axially longer reactor lengthsmay experience increased pressure drops through the reactor. However forsuch embodiments, the porous and/or permeable media may include, forexample, at least one of a packed bed, an arrangement of tiles, apermeable solid media, a substantially honeycomb-type structure, afibrous arrangement, and a mesh-type lattice structure.

In some aspects, the reverse flow reactor can include some type ofequipment or method to direct a flow stream of one of the reactants intoa selected portion of the conduits. In the exemplary embodiment of FIG.2, a gas distributor 31 can direct a second gas stream 32 to second gasstream channels that are substantially isolated from or not in fluidcommunication with the first gas channels, here illustrated as channels33. The result can be that at least a portion of gas stream 33 is keptseparate from gas stream 30 during axial transit of the recuperator 27.In some aspects, the regenerative bed(s) and/or monolith(s) of therecuperator zone can comprise channels having a gas or fluid barrierthat isolates the first reactant channels from the second reactantchannels. Thereby, both of the at least two reactant gases that transitthe channel means may fully transit the regenerative bed(s), to quenchthe regenerative bed, absorb heat into the reactant gases, beforecombining to react with each other in the combustion zone.

In various aspects, gases (including fluids) 30 and 32 can each comprisea component that reacts with a component in the other reactant 30 and32, to produce an exothermic reaction when combined. For example, eachof the first and second reactant may comprise one of a fuel gas and anoxidant gas that combust or burn when combined with the other of thefuel and oxidant. By keeping the reactants substantially separated, thelocation of the heat release that occurs due to exothermic reaction canbe controlled. In some aspects “substantially separated” can be definedto mean that at least 50 percent, or at least 75 percent, or at least 90percent of the reactant having the smallest or limitingstoichiometrically reactable amount of reactant, as between the firstand second reactant streams, has not become consumed by reaction by thepoint at which these gases have completed their axial transit of therecuperator 27. In this manner, the majority of the first reactant 30can be kept isolated from the majority of the second reactant 32, andthe majority of the heat release from the reaction of combiningreactants 30 and 32 can take place after the reactants begin exiting therecuperator 27. The reactants can be gases, but optionally somereactants may comprise a liquid, mixture, or vapor phase.

The percent reaction for these regeneration streams is meant the percentof reaction that is possible based on the stoichiometry of the overallfeed. For example, if gas 30 comprised 100 volumes of air (80 volumes N₂and 20 Volumes O₂), and gas 32 comprised 10 volumes of hydrogen, thenthe maximum stoichiometric reaction would be the combustion of 10volumes of hydrogen (H₂) with 5 volumes of oxygen (O₂) to make 10volumes of H₂O. In this case, if 10 volumes of hydrogen were actuallycombusted in the recuperator zone (27), this would represent 100%reaction of the regeneration stream. This is despite the presence ofresidual un-reacted oxygen, because in this example the un-reactedoxygen was present in amounts above the stoichiometric requirement.Thus, in this example the hydrogen is the stoichiometrically limitingcomponent. Using this definition, less than 50% reaction, or less than25% reaction, or less than 10% reaction of the regeneration streams canoccur during the axial transit of the recuperator (27).

In various aspects, channels 28 and 33 can comprise ceramic (includingzirconia), alumina, or other refractory material capable of withstandingtemperatures exceeding 1200° C., or 1400° C., or 1600° C. Additionallyor alternately, channels 28 and 33 can have a wetted area between 50ft⁻¹ and 3000 ft⁻¹, or between 100 ft⁻¹ and 2500 ft⁻¹, or between 200ft⁻¹ and 2000 ft⁻¹.

Referring again briefly to FIG. 1, the reactor system can includes afirst reactor 7 containing a first end 9 and a second end 11, and asecond reactor 1 containing a primary end 3 and a secondary end 5. Theembodiments illustrated in FIGS. 1 and 2 are merely simple illustrationsprovided for explanatory purposes only and are not intended to representa comprehensive embodiment. Reference made to an “end” of a reactormerely refers to a distal portion of the reactor with respect to anaxial mid-point of the reactor. Thus, to say that a gas enters or exitsan “end” of the reactor, such as end 9, means merely that the gas mayenter or exit substantially at any of the various points along an axisbetween the respective end face of the reactor and a mid-point of thereactor, but more preferably closer to the end face than to themid-point. Thereby, one or both of the first and second reactant gasescould enter at the respective end face, while the other is supplied tothat respective end of the reactor through slots or ports in thecircumferential or perimeter outer surface on the respective end of thereactor.

EXAMPLE 1A—PREPARATION OF CERAMIC MONOLITH WITH CATALYTIC ACTIVITY FORREFORMING

Ceramic monoliths have a size of 1.0 inch (˜2.5 cm) long×0.5 inch (˜1.3cm) diameter were extruded at temperatures of 1300° C. and 1400° C. Themonoliths were composed of 25 wt % nickel oxide (NiO) and 75 wt %alumina, titania, and bentonite. The extruded monoliths had a 400 cpsi(cells per square inch) and an open frontal area of either 35% or 52%.The monoliths included a weight ratio of alumina to nickel oxide ofroughly 3.0. Nominally, the monoliths were composed of 22.1% NiO, 67.8%Al₂O₃, 8.4% SiO₂, 0.1% Fe₂O₃, 0.3% CaO, 0.2% MgO, <0.1% K₂O/Na₂O, and1.0% TiO₂ as measured by x-ray fluorescense (XRF). The NiAl₂O₄ monolithwas sintered at 1400° C., which resulted in a 8.3 wt % water absorption.

Table 1 shows a comparison of the properties of the NiAl₂O₄ ceramicmonoliths with monoliths formed from either α-Al₂O₃ or NiO. As shown inTable 1, the NiAl₂O₄ monoliths provide a higher volumetric heat capacitythan an α-Al₂O₃ having a similar open frontal area. In Table 1, OFArefers to open frontal area; C_(P) is the heat capacity at roomtemperature (˜20° C.), and VHC is the volumetric heat capacity at roomtemperature.

TABLE 1 Monolith Properties Density Material OFA Porosity (g/cm³) C_(P)(J/g/K) VHC (J/cm³) α-Al₂O₃ 55% 30%  3.9 0.78 0.96 α-Al₂O₃ 55% 0% 3.90.78 1.37 α-Al₂O₃ 35% 0% 3.9 0.78 1.98 NiO 35% 0% 6.7 0.68 2.96 25 wt %NiO/75 35% 0% 2.23 wt % α-Al₂O₃ 25 wt % NiO/75 52% 8.3%  1.51 wt %α-Al₂O₃

EXAMPLE 1B Characterization of Ceramic Monolith

The ceramic monolith sintered at 1400° C. with an open frontal area of52% was further characterized prior to evaluation of the monolith forreforming activity. FIG. 3 shows an SEM image at a first magnificationlevel (50×) that shows details regarding the wall structure between thecells of the monolith. The SEM image in FIG. 3 shows that the ceramicmaterial has some porosity.

FIG. 4 shows an SEM image at a higher magnification level (3000×) thatshows additional details regarding the surface structure of a honeycombwall between the cells of the ceramic material. As shown in FIG. 4, thesurface of the wall appears to be composed of a large number of grainsor particles, as opposed to having a larger scale crystalline structure.This is believed to be due to the honeycomb wall being composed ofseveral distinct phases of materials. This can be further seen in FIG.5, which shows an X-ray diffraction characterization of the portion ofthe honeycomb wall shown in FIG. 4. As shown in FIG. 5, the honeycombwall is composed of both NiAl₂O₄ (peaks designated as “A”) as well asleftover alumina (“B”) and mullite (“C”). The alumina and mullite phasesare present because the ceramic composition includes a molar excess ofalumina relative to the stoichiometric amount of alumina needed to forma solid nickel aluminate structure. The sample contains a molar ratio of4.5 Al:Ni while a pure nickel aluminate structure has a molar ratio of2:1. As a result, the sintered ceramic structure includes a substantialamount of alumina that is distinct from the nickel aluminate. Themullite is believed to be primarily formed by a reaction betweensilicate in bentonite and alumina during high temperature sintering.After sintering and prior to exposure to a reforming environment, themonolith is composed of 58% NiAl₂O₄, 21% Al₂O₃, and 21% mullite.

EXAMPLES 2 to 11 Activity of Ceramic Monolith for Reforming

The performance of the ceramic monolith from Example 1 was evaluated formethane reforming with both steam and carbon dioxide in a lab scalefixed-bed, down-flow reactor. The 1.0 inch (˜2.5 cm)×0.5 inch (˜1.3 cm)monolith was wrapped in a high temperature alumina cloth to preventbypassing and loaded into a quartz reactor with an inlet diameter ofapproximately 0.6 inches (˜1.5 cm). The space velocities were calculatedbased on the monolith as if the monolith was a solid cylinder. Athermocouple was located directly above the top of and directly belowthe bottom of the catalytic monolith. The methane and carbon dioxideconversion was determined by the disappearance of the reactant. Thesyngas ratio was calculated as the molar ratio of H₂ and CO in theproducts. All conversion for continuous flow experiments are reportedafter 1 hour of lineout. All cycle conversions are reported after 100cycles at that temperature except when specifically stated. The nitrogenincluded in each run is used as an internal standard for gaschromatograph analysis. Table 2 shows the conditions and resultscorresponding to Examples 2-11.

TABLE 2 Reforming Activity of Monolith Type of Reforming GHSVTemperature CH₄ Example Cycling (H₂O + CO₂:CH₄) (h⁻¹ × 10⁻³) (° C.)Conversion H₂/CO 2 N Bi (1.1:1) 10 800  0% 3 N Bi (1.1:1) 20 800  0% 4 NBi (1.1:1) 20 900 11% 2.4 5 N Bi (1.1:1) 20 1000 25% 2.3 6 N Bi (1.1:1)10 800 45% 2.2 7 N Bi (1.1:1) 20 800 21% 2.3 8 Y Dry (1.1:1) 20 800 34%0.6 9 Y Dry (1.1:1) 20 900 46% 0.7 10 Y Dry (1.1:1) 20 1000 60% 0.8 11 YDry (1.1:1) 20 800 35% 0.6

Examples 2 and 3 show the initial experiments on the monolith, which had400 cells per square inch (cpsi) and was composed of 25 wt % NiO and 75%bentonite. The simultaneous reforming of methane and carbon dioxide(bi-reforming) was performed on the catalytic monolith with a spacevelocity of either 10,000 hr⁻¹ (Example 2) or 20,000 hr⁻¹ (Example 3)based on total monolith volume and a gas composition of 42.9% CH₄, 31.4%H₂O, 15.7% CO₂, and 10% Nz. At a temperature of 800° C. and spacevelocity of 20,000 hr⁻¹, the monolith had no appreciable conversionafter 60 min of TOS. While a small amount of hydrogen was observed atthe start of reaction, there was no quantifiable production of CO.Without being bound by any particular theory, it is believed that anycatalytic sites that were exposed at 800° C. to the bi-reforming feed tolikely coked immediately and became in-active for the methane reformingreaction. Between the 800° C. and 900° C. experiments (i.e., betweenExample 3 and Example 4), and after each subsequent condition change(i.e., between each subsequent example number), the monolith was exposedto a flow of 5% O₂/N₂ for 10 min. After exposure to the oxygen, themonolith was catalytically active at 900° C. (Example 4) and 1000° C.(Example 5) with a conversion of 11 wt % and 25 wt % of the methane inthe feed, respectively. Upon revisiting the 800° C. conditions atidentical flow rates (Examples 6 and 7), the monolith had catalyticactivity with significant methane conversion in stark contrast to thelack of catalytic activity at the beginning of Example 2 or Example 3.

Example 8 shows an experiment for the cycling dry reforming of methanewith carbon dioxide at a space velocity of 20,000 h⁻¹ and a gascomposition of 43.1% CH₄, 46.9% CO₂, and 10% Nz. The cycling dryreforming experiments include an extra step where the feed is introducedfor 1 min followed by a 7 sec nitrogen purge and then a 5% O₂/N₂ feed isintroduced for 1 min followed by an additional 7 sec nitrogen purge.This cycle is repeated for about 100 cycles to line out the conversionexcept when noted. Results for cycling dry reforming at 800° C., 900°C., and 1000° C. (oven set temperatures) are shown and the conversionincreases slightly with increasing temperature (Examples 8-10). When themonolith is returned to the identical 800° C. dry reforming cyclingcondition (Example 11), the conversion remains constant. Thus, thecatalytic monolith was activated by the exposure to oxidative conditionsand achieved significantly higher conversion than before its exposure tooxygen.

EXAMPLE 12 Additional Analysis of Example Reforming Results

The nature of the in-situ catalytic activity of the combined nickeloxide, alumina, titania and bentonite ceramic monolith was investigatedby characterizing the monolith after the final reforming process(Example 11). The ceramic monolith was not exposed to an oxidizingenvironment after Example 11. SEM images were obtained of thepost-reducing environment monolith. The SEM images of the monolith priorto exposure to the cyclic reaction environment, as shown in FIG. 4, andafter exposure to the cyclic reaction environment, as shown in FIG. 6,show a remarked difference in appearance. The monolith surface in FIG. 4is characterized by a nickel aluminate spinel with additional aluminaand mullite regions. By contrast, after exposure to the cyclic reactionenvironment, the resulting surface shown in FIG. 6 includes a mixture ofalumina, mullite that is primarily formed by a reaction between silicatein bentonite and alumina, and fine metallic nickel nanoparticles. Thepresence of the nickel particles is confirmed by the energy dispersiveX-ray spectroscopy spectrum shown in FIG. 7, which shows the presence ofboth metallic nickel and alumina.

The production of the nickel nanoparticles is unexpected from the nickelaluminate spinel phase that was produced by calcination at 1400° C. Moregenerally, it is unexpected that the surface of a ceramic including adopant oxide can be converted to a surface including dopant metalparticles, even though the ceramic has previously been calcined and/orsintered at temperatures of 500° C. or more, or 800° C. or more, or1000° C. or more. It is also unexpected that the monolith substantiallyretains its shape/structure after conversion from nickel aluminate tonickel supported on alumina. Without being bound by any particulartheory, the dispersed nickel nanoparticles on the ceramic monoliths arebelieved to be responsible for the catalytic activity of the ceramicmonolith. The dispersed nickel particles can correspond to nickelparticles formed after the initial reducing step, or nickel particlesformed during any subsequent reducing step in the cyclic reactionenvironment. The ability to form nickel particles in-situ avoids theneed to washcoat the monolith with an alternative metal, but anadditional metal, such as rhodium, may optionally be added to increasecatalytic activity. After exposure to the cyclic reaction environment,the monolith is composed of 18% Ni, 60% Al₂O₃, and 22% mullite.

FIG. 8 shows an illustration created based on data from a transmissionelectron microscope (TEM) image at a still higher level ofmagnification. The illustration in FIG. 8 is based on an SEM image fromanother region of the same monolith shown in FIGS. 4 and 6. In FIG. 8,in addition to showing a Ni particle 805 on a surface including bothalumina 830 and mullite 840 phases, a second particle 815 including avariety of phases is also present. The core of the second particle 815is composed of a combination of alumina and nickel aluminate, withadditional smaller particles on the surface. The variety of smallerparticles on the surface of particle 815 correspond to both Ni metalparticles 822 and Ni-deficient nickel aluminate (Ni_(1-x) Al₂O₄particles) 824. Thus, at least some mixed oxide that includes dopantmetal oxide is still present on the surface after activation of thecatalyst and exposure to cyclic reducing and oxidizing conditions.

Additional Embodiments

Embodiment 1. A method for reforming a hydrocarbon-containing stream,comprising: exposing a hydrocarbon-containing stream to a catalystcomposition in the presence of at least one of H₂O and CO₂ underreforming conditions comprising a temperature of 500° C. or more to forma reformed product comprising H₂, the catalyst composition comprising0.1 wt % or more of dopant metal particles supported on 50 wt % to 99 wt% of one or more structural oxides, the one or more dopant metalscorresponding to dopant metal oxides having a Gibbs free energy offormation at 800° C. that is greater than a Gibbs free energy offormation at 800° C. for the one or more structural oxides by 200 kJ/molor more, the particles of the one or more dopant metals having anaverage characteristic length of 10 um or less, the dopant metal oxidecomprising an oxide of Ni, Rh, Ru, Pd, Pt, Ir, or a combination thereof;and exposing the catalyst composition to a stream comprising fuel and0.1 vol % or more of 02 under combustion conditions to heat anenvironment for the catalytic composition to a temperature of 500° C. ormore.

Embodiment 2. The method of Embodiment 1, wherein the method furthercomprises: exposing an initial composition comprising 0.1 wt % or moreof at least one dopant metal oxide and 50 wt % to 99 wt % of the one ormore structural oxides, to a reducing environment comprising atemperature of 500° C. to 1400° C. to form the catalyst compositioncomprising the dopant metal particles supported on the one or morestructural oxides; and exposing the catalyst composition to an oxidizingenvironment comprising a temperature of 500° C. to 1400° C., theexposing the hydrocarbon-containing stream to the catalyst compositionbeing performed after the exposing the catalyst composition to theoxidizing environment.

Embodiment 3. The method of Embodiment 2, a) wherein exposing theinitial composition to the reducing environment comprises exposing theinitial composition to a hydrocarbon-containing stream in the presenceof at least one of H₂O and CO₂ under reforming conditions comprising atemperature of 500° C. or more.

Embodiment 4. The method of Embodiment 2 or 3, wherein exposing thecatalyst composition to an oxidizing environment comprises exposing thecatalyst composition to a stream comprising 0.1 vol % or more of O₂ at aregeneration temperature of 500° C. or more for a regeneration timeperiod.

Embodiment 5. The method of any of the above embodiments, whereinexposing the hydrocarbon-containing stream to the catalyst compositioncomprises: introducing a hydrocarbon-containing stream into a first endof a reactor comprising a monolith comprising the catalyst composition;and exposing the hydrocarbon-containing stream to the catalystcomposition in the presence of at least one of H₂O and CO₂ underreforming conditions comprising a temperature of 800° C. or more to forma reformed product comprising Hz.

Embodiment 6. The method of Embodiment 5, further comprising:withdrawing at least a portion of the reformed product from a firstlocation different from the first end of the reactor; introducing aregeneration stream comprising fuel and a stream comprising O₂ into thereactor, at least a portion of the stream comprising fuel and/or thestream comprising O₂ being introduced into a second end of the reactor;combusting the stream comprising fuel and the stream comprising oxygenunder combustion conditions to form a combustion product stream, thecombustion product stream optionally comprising 0.1 vol % or more of O₂;exposing the combustion product stream to the catalyst composition totransfer heat to the catalyst composition; and withdrawing at least aportion of the combustion product stream from the reactor.

Embodiment 7. The method of Embodiment 5 or 6, wherein thehydrocarbon-containing stream is exposed to the catalyst composition ina reverse flow reactor.

Embodiment 8. The method of any of the above embodiments, wherein thecatalyst composition further comprises an additional catalytic metal,the additional catalytic metal comprising Ni, Rh, Ru, Pd, Pt, Ir, or acombination thereof.

Embodiment 9. The method of any of the above embodiments, wherein thehydrocarbon-containing stream comprises 5 wt % or more C₂₊ hydrocarbons,40 wt % or more methane, or a combination thereof; or wherein the methodfurther comprises periodically exposing the catalyst composition to anoxidizing stream comprising 0.1 vol % or more of O₂ at a temperature of500° C. or more for an oxidizing time period; or a combination thereof.

Embodiment 10. The method of any of the above embodiments, wherein thedopant metal particles comprise 1.0 wt % or more of Ni particles, andwherein the one or more structural oxides comprise Al₂O₃.

Embodiment 11. The method of Embodiment 10, wherein the catalystcomposition further comprises NiO, NiAl₂O₄, or a combination thereof.

Embodiment 12. The method of Embodiment 10 or 11, wherein the initialcomposition comprises 40 wt % or more Al₂O₃.

Embodiment 13. The method of any of the above embodiments, i) whereinthe catalyst composition comprises a monolith having a cell density ofmore than 900 cells per square inch, ii) wherein the catalystcomposition comprises a honeycomb monolith, iii) wherein the initialcomposition is formed by extrusion, or iv) a combination of two or moreif i), ii), and iii).

Embodiment 14. The method of any of the above embodiments, wherein thecatalyst composition comprises a volumetric heat capacity of 140 kJ/cm³or more.

Embodiment 15. The method of any of the above embodiments, wherein theone or more structural oxides comprise at least one mixed structuraloxide phase, or wherein the catalyst composition further comprises amixed oxide phase including an oxide of the one or more dopant metalsand at least one structural oxide.

While the present invention has been described and illustrated byreference to particular embodiments, those of ordinary skill in the artwill appreciate that the invention lends itself to variations notnecessarily illustrated herein. For this reason, then, reference shouldbe made solely to the appended claims for purposes of determining thetrue scope of the present invention.

The invention claimed is:
 1. A method for reforming ahydrocarbon-containing stream, comprising: exposing an initial ceramiccomposition comprising 0.1 wt % or more of at least one dopant metaloxide and 50 wt % to 99 wt % of one or more structural oxides, to areducing environment comprising a temperature of 500° C. to 1400° C. toform a catalyst composition comprising dopant metal particles supportedon the one or more structural oxides, the one or more dopant metalscorresponding to dopant metal oxides having a Gibbs free energy offormation at 800° C. that is greater than a Gibbs free energy offormation at 800° C. for the one or more structural oxides by 200 kJ/molor more, the particles of the one or more dopant metals having anaverage characteristic length of 10 μm or less, the dopant metal oxidecomprising an oxide of Rh, Ru, Pd, Pt, Ir, or a combination thereof;exposing the catalyst composition to an oxidizing environment comprisinga temperature of 500° C. to 1400° C.; exposing a hydrocarbon-containingstream to the catalyst composition in the presence of at least one ofH₂O and CO₂ under reforming conditions comprising a temperature of 500°C. or more to form a reformed product comprising H₂, the exposing thehydrocarbon-containing stream to the catalyst composition beingperformed after the exposing the catalyst composition to the oxidizingenvironment; and exposing the catalyst composition to a streamcomprising fuel and 0.1 vol % or more of O₂ under combustion conditionsto heat an environment for the catalytic composition to a temperature of500° C. or more.
 2. The method of claim 1, wherein the one or morestructural oxides comprise at least one mixed structural oxide phase. 3.The method of claim 1, wherein the catalyst composition furthercomprises a mixed oxide phase including an oxide of the one or moredopant metals and at least one structural oxide.
 4. A method forreforming a hydrocarbon-containing stream, comprising: exposing aninitial ceramic composition comprising 1.0 wt % or more of Ni in anoxide form and 50 wt % to 99 wt % of one or more structural oxides, theone or more structural oxides comprising Al₂O₃, to a reducingenvironment comprising a temperature of 500° C. to 1400° C. to form acatalyst composition comprising Ni particles supported on Al₂O₃;exposing the catalyst composition to an oxidizing environment comprisinga temperature of 500° C. to 1400° C.; exposing a hydrocarbon-containingstream to the catalyst composition in the presence of at least one ofH₂O and CO₂ under reforming conditions comprising a temperature of 800°C. or more to form a reformed product comprising H₂, the exposing thehydrocarbon-containing stream to the catalyst composition beingperformed after the exposing the catalyst composition to the oxidizingenvironment; and exposing the catalyst composition to a streamcomprising fuel and 0.1 vol % or more of O₂ under combustion conditionsto heat an environment for the catalyst catalytic composition to atemperature of 800° C. or more.
 5. The method of claim 4, whereinexposing the initial ceramic composition to the reducing environmentcomprises exposing the initial ceramic composition to ahydrocarbon-containing stream in the presence of at least one of H₂O andCO₂ under reforming conditions comprising a temperature of 500° C. ormore.
 6. The method of claim 4, wherein exposing the catalystcomposition to an oxidizing environment comprises exposing the catalystcomposition to a stream comprising 0.1 vol % or more of O₂ at aregeneration temperature of 500° C. or more for a regeneration timeperiod.
 7. The method of claim 4, i) wherein the catalyst compositioncomprises a monolith having a cell density of more than 900 cells persquare inch, ii) wherein the catalyst composition comprises a honeycombmonolith, iii) wherein the initial composition is formed by extrusion,or iv) a combination of two or more if i), ii), and iii).
 8. The methodof claim 4, wherein the catalyst composition comprises a volumetric heatcapacity of 140 kJ/cm³ or more.
 9. The method of claim 4, wherein thecatalyst composition further comprises NiO, NiAl₂O₄, or a combinationthereof.
 10. The method of claim 4, wherein the initial ceramiccomposition comprises 40 wt % or more Al₂O₃.
 11. The method of claim 4,wherein the initial ceramic composition comprises an initial ceramiccomposition sintered at a temperature of 1200° C. or higher.
 12. Amethod for reforming a hydrocarbon-containing stream, comprising:performing a cyclic reforming process, the cyclic reforming processcomprising: introducing a hydrocarbon-containing stream into a first endof a reactor comprising a monolith comprising a catalyst composition,the catalyst composition comprising 0.1 wt % or more of dopant metalparticles supported on 50 wt % to 99 wt % of one or more structuraloxides, the one or more dopant metals corresponding to dopant metaloxides having a Gibbs free energy of formation at 800° C. that isgreater than a Gibbs free energy of formation at 800° C. for the one ormore structural oxides by 200 kJ/mol or more, the particles of the oneor more dopant metals having an average characteristic length of 10 μmor less, the dopant metal oxide comprising an oxide of Rh, Ru, Pd, Pt,Ir, or a combination thereof; exposing the hydrocarbon-containing streamto the catalyst composition in the presence of at least one of H₂O andCO₂ under reforming conditions comprising a temperature of 800° C. ormore to form a reformed product comprising H₂; withdrawing at least aportion of the reformed product from a first location different from thefirst end of the reactor; introducing a regeneration stream comprisingfuel and a stream comprising O₂ into the reactor, at least a portion ofthe stream comprising fuel, at least a portion of the stream comprisingO₂, or a combination thereof being introduced into a second end of thereactor; combusting the stream comprising fuel and the stream comprisingoxygen under combustion conditions to form a combustion product stream;exposing the combustion product stream to the catalyst composition totransfer heat to the catalyst composition; and withdrawing at least aportion of the combustion product stream from the reactor.
 13. Themethod of claim 12, wherein the catalyst composition further comprises amixed oxide phase including an oxide of the one or more dopant metalsand at least one structural oxide.
 14. A method for reforming ahydrocarbon-containing stream, comprising: performing a cyclic reformingprocess, the cyclic reforming process comprising: introducing ahydrocarbon-containing stream into a first end of a reactor comprising amonolith comprising a catalyst composition, the catalyst compositioncomprising 1.0 wt % or more of Ni particles, NiO, NiAl₂O₄, or acombination thereof, supported on 50 wt % to 99 wt % of one or morestructural oxides, the one or more structural oxides comprising Al₂O₃;exposing the hydrocarbon-containing stream to the catalyst compositionin the presence of at least one of H₂O and CO₂ under reformingconditions comprising a peak temperature of 800° C. or more to form areformed product comprising H₂; withdrawing at least a portion of thereformed product from a first location different from the first end ofthe reactor; introducing a regeneration stream comprising fuel and astream comprising O₂ into the reactor, at least a portion of the streamcomprising fuel and/or the stream comprising O₂ being introduced into asecond end of the reactor; combusting the stream comprising fuel and thestream comprising oxygen under combustion conditions to form acombustion product stream; exposing the combustion product stream to thecatalyst composition to transfer heat to the catalytic composition, atleast a portion of the catalyst composition being heated to a peaktemperature of 1000° C. or higher; and withdrawing at least a portion ofthe combustion product stream from the reactor.
 15. The method of claim14, wherein the hydrocarbon-containing stream is exposed to the catalystcomposition in a reverse flow reactor.
 16. The method of claim 15,wherein the hydrocarbon-containing stream comprises 5 wt % or more C₂₊hydrocarbons, 40 wt % or more methane, or a combination thereof.
 17. Themethod of claim 15, wherein the catalyst composition further comprisesan additional catalytic metal, the additional catalytic metal comprisingRh, Ru, Pd, Pt, Ir, or a combination thereof.
 18. The method of claim14, wherein the combustion product stream comprises 0.1 vol % or more ofO₂., the combustion product stream being exposed to the catalystcomposition under conditions that comprise a temperature of 500° C. ormore.
 19. The method of claim 14, wherein the method further comprisesperiodically exposing the catalyst composition to an oxidizing streamcomprising 0.1 vol % or more of O₂ at a temperature of 500° C. or morefor an oxidizing time period.
 20. The method of claim 14, wherein thereforming conditions comprise a peak temperature in a reforming zone of1000° C. or higher.